Four calculators, one panel.
Pick a mode below — everything recalculates live as you type, and every result explains itself with the formula it came from.
The object’s mass — kilograms by default; switch to g, lb, oz or tonnes if that’s what you have.
Speed with direction — a minus sign means the opposite direction. Units: m/s, km/h, mph or ft/s.
The momentum you already know — used when solving for mass or velocity.
The average push or pull during the event — negative means the opposite direction.
How long the force keeps acting — must be positive.
The impulse you already know — used when solving for force or time.
The object whose velocity is changing.
Where the object starts — a negative value means it’s already moving the other way.
Where the object ends up.
Leave this blank to skip the force; enter it to also get the average force F = Δp ÷ Δt.
All three conserve momentum — they differ in what happens to kinetic energy.
Motion is along one line — a negative value means moving the other way (head-on hit).
0 m/s = standing still before the impact.
What object 1 ends up doing — the tool solves object 2’s final velocity from conservation of momentum.
Four steps, zero friction.
Built to be obvious on the first try — no manual, no reset-button hunting, results update the moment you type.
Choose your tab
Momentum, impulse, change in momentum or collisions — the four tabs cover the whole topic, from homework checks to lab reports.
Type any two values
The third is solved instantly. Pick units from the dropdowns, and use a minus sign for velocities pointing the other way.
Answer plus context
Unit conversions, kinetic energy or average force where relevant, and the formula with your own numbers substituted in.
Take it with you
Hit COPY for a plain-text summary to paste into notes or homework — and re-check any result against the formula line by hand.
Every formula behind the tool.
The six equations the calculator uses — the same ones shown with your numbers substituted in every result.
Momentum
Mass in kilograms times velocity in metres per second gives momentum in kg·m/s — a vector pointing the way the object moves.
Impulse
A force in newtons acting for a time in seconds. The impulse is the momentum change the force delivers, measured in N·s.
Impulse–momentum theorem
The same change in momentum seen from either side: a velocity change over time, or a force acting for a time.
Conservation of momentum
With no outside forces, total momentum before a collision equals total momentum after — always, elastic or not.
Perfectly inelastic collision
The objects stick together and move at one speed — the momentum-weighted average of the two starting velocities.
Elastic collision (1D)
v2' = ((m2−m1)u2 + 2m1u1) ÷ (m1+m2)
Both momentum and kinetic energy come out conserved — billiard-ball physics. Equal masses simply swap velocities.
Questions students actually ask.
Short, exam-ready answers. If yours isn’t here, the formula cards above probably cover it.
How do I calculate momentum?+
Multiply mass by velocity: p = m × v. A 1,200 kg car travelling at 25 m/s has p = 1,200 × 25 = 30,000 kg·m/s. Momentum is a vector — direction matters, so a minus sign means the opposite direction. Mode 01 solves for any missing variable and converts units for you.
What are the units of momentum?+
The SI unit is the kilogram metre per second (kg·m/s), numerically identical to the newton-second (N·s). Imperial uses lb·ft/s and CGS uses g·cm/s. The calculator accepts all of these and converts between them automatically.
What is the difference between momentum and impulse?+
Momentum is a property an object has at one moment (mass × velocity). Impulse is the change you make to it: a force acting over a time interval, J = F × Δt. The impulse–momentum theorem says they are numerically equal — J = Δp — so a 50 N push lasting 4 s changes momentum by 200 kg·m/s.
Can momentum be negative?+
Yes. Momentum is a vector, so its sign shows direction along a chosen axis. A car braking from +25 m/s to 0 m/s has Δp = m(0 − 25) = −30,000 kg·m/s — the minus just means the change points backwards. In collisions, enter negative velocities for objects moving the other way.
What does conservation of momentum mean?+
If no outside force acts on a system, its total momentum stays constant: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂. This holds for every collision — elastic or not — which is why the after-speeds can be predicted from the before-speeds. The Collisions tab checks it and shows momentum before and after.
What is the difference between elastic and inelastic collisions?+
Momentum is conserved in both. In a perfectly elastic collision kinetic energy is also conserved — objects bounce apart unchanged, like billiard balls. In an inelastic collision some kinetic energy becomes heat, sound or deformation; if the objects stick together and move as one, it’s perfectly inelastic. The calculator shows kinetic energy before and after so you can see exactly how much was lost.
How do I convert units before calculating?+
You don’t need to — pick any unit from the dropdowns and the calculator converts internally. If doing it by hand: km/h ÷ 3.6 = m/s, mph × 0.44704 = m/s, ft/s × 0.3048 = m/s, lb × 0.45359237 = kg, tonne × 1000 = kg.
Is this calculator free, and is my data sent anywhere?+
It is completely free and runs entirely in your browser — nothing you type is uploaded, logged, or sent to a server. No account, no sign-up, no limits.